Diagenesis and transformation of aquatic dissolved organic matter in Nova Scotia freshwaters

Abstract

<p>The acid-base and structural chemistry of freshwater dissolved organic matter (DOM) is known to vary with time and location. The purpose of this dissertation is to show how the chemical quality of DOM in temperate streams, wetlands and lakes of the Kejimkujik National Park area in central Nova Scotia varies over an annual cycle and how the changes in quality are related to DOM formation and diagenesis. New techniques were developed and used to better define the chemical quality DOM. A titration method described by Brassard et al. (1990) allowed the description of the acid-base characteristics of DOM. A reverse osmosis method is also described for the concentration of DOM without its fractionation to allow structural determination by ¹³C NMR of whole material. The results indicate that the chemical quality of DOM found in freshwaters is not similar to that found in soils. This difference suggests that interactions between soils, biology and hydrology modify the DOM in streams. A laboratory experiment suggests that the most likely pathway of DOM formation is the breakdown of plant structural material into aliphatic material with subsequent aromatic formation via semi-quinone and quinone. Comparison of incubation experiments with field results also shows that DOM acidity in natural water decreases with time caused by biological and chemical oxidative processes. Theoretical considerations indicate that the acidity of DOM does not follow the simple relationship suggested by Oliver et al. (1983) because of differences in source material and diagenetic processes, as well as the influence of inorganic cations and anions which until now have been assumed to be uncomplexed with organic matter.</p>